try allowing DBusActivatable

lib/controllers/notification.dart

@@ -98,6 +98,10 @@ class NotificationController
                   name: "image-path",
                   value: LinuxHintStringValue(icon.path),
                 ),
+                .new(
+                  name: "desktop-entry",
+                  value: LinuxHintStringValue("nexus.federated.nexus"),
+                ),
               ],
       ),
       // TODO: See if icons can be added to iOS, macOS, and Windows notifications (#68)

linux/nexus.federated.nexus.desktop

@@ -6,5 +6,6 @@ Exec=nexus %u
 Icon=nexus
 Terminal=false
 Type=Application
+DBusActivatable=true
 Categories=Chat;Network;InstantMessaging;
 MimeType=x-scheme-handler/nexus.federated.nexus;